Process for the production of polyvinyl alcohol yarns and films from polyesters



.Uflitc States Pate PROCESS FOR THE PRODUCTION OF POLYVINYL g cg goL YARNS AND FILMS FROM POLY- Emile Clment Cottet andAndr Claude Ducros, Lyon, France, assignors to Societe des Usines Chimiques Rhone-Poulenc, Paris, France, a corporation of France No Drawing. Application June 11, 1958 Serial No. 741,225

The present invention relates to a process for the production of polyvinyl alcohol yarns and films.

, It is known to deacetylate (saponify) polyvinyl acetate to. polyvinylalcohol and to convert the product obtained into yarns or'films. The deacetylation is effected in a solution in an organic solvent, or an aqueous emulsion, of polyvinyl acetate to which the deacetylation agent has been added. A precipitate of polyvinyl alcohol is obtained if the reaction medium is an organic solvent, while if the polyvinyl acetate is deacetylated as an aqueous emulsion, the polyvinyl alcohol is obtained in solution in the water. 1 Sushanaqueous solution, or one obtained by dissolving in'water a polyvinyl alcohol precipitate, may be converted into yarns or films by known means, which however involve a series of complicated and costly operations.

It has now been found, and this ,forms' the subject of the present invention, that it is possible to obtain yarns and films of polyvinyl alcohol by saponifying yarns and films of polyvinyl esters, more especially polyvinyl acetate, while preserving their structure, using as the saponifying agent a solution of an alkali metal alcoholate in methanol, the concentration of the alkali metal alcoholate in the methanol being at least 8.5 molar percent, and the molecular weight of the polyvinyl ester being such that a 5% (by weight) solution thereof in a mixture of 15 volumes of 95% (by volume) alcohol and 85 volumes of ethyl acetate at 20 C. is at least 8 centipoises.

It isquite surprising thatsuchamedium permits the deacetylation of polyvinyl preserving their structure, because methanol is in fact a solvent for polyvinyl acetate. It must be presumed that the rate of deacetylation, by which the polyvinyl acetate is converted into polyvinyl alcohol which is insoluble in methanol, is greater than the rate of dissolution of the polyvinyl acetate in methanol.

It has already been proposed to spin polyvinyl acetate by known processes, notably from solutions in organic solvents, and to deacetylate the yarns obtained without destroying their structure, by using as the deacetylating agent a caustic alkali solution in a medium which is not a solvent for polyvinyl acetate, such as a higher alcohol and especially hexyl alcohol, but this process, in contradistinction to that forming the subject of the present invention, requires the use of agents (the higher alcohols) which are not very readily accessible and which, moreover, give rates of deacetylation which are much too low to be compatible with continuous operation, such as is necessary for economic industrial production.

The saponifying baths employed in the present invention may be obtained by dissolving an alkali metal in methanol or by the azeotropic dehydration of a solution of a caustic alkali in methanol, Instead of an alkali methylate, it is equally possible to employ solutions in acetate yarns and films while methanol of alkali alcoholates prepared especially with other lower alcohols, such as ethyl, propyl and butyl elem hols. The content of alkali metal alcoholate in the bath is preferably 8.5-45% molar, e.g. between about 2% and 10% by weight (expressed as alkali metal) in the case of sodium.

By yarns are meant either the multi-filament yarns obtained by the combination of primary filaments spun through a multi-hole spineret or mono-filaments obtained by spinning through a spinneret having a single hole.

Yarns and films of a diameter or thickness of 0.02 to 0.05 mm. may be saponified and converted into polyvinyl alcohol yarns and films which are completely soluble in hot water by passing them for several minutes through a bath containing 12% of sodium methylate (5% Na) at a temperature of 20-25 C. The rapidity of saponification at that temperature permits of performing it continuously under normal industrial conditions, and moreover it may be increased by raising the temperature of the saponifying .bath, which may be anything between room temperature and the boiling temperature of the bath, i.e. about C. The 12% sodium methylate solution in methanol may be replaced by a solution of another alkali metalmethylate of substantially equal molecular concentration, for example an 8% solution of lithium methylate or a 15% solution of potassium methylate in methanol.

The best results are obtained by passing the yarns or films to saponilied, first through a tank containing saponifying solution at room temperature, e.g. 20-25 C., and then through a second tank containing saponifying solution at a higher temperature, preferably 4070 C., e.g. 60 C Instead of polyvinyl acetate, other homopoly meric esters and vinylic copolymers may be employed, provided that they are readily saponifiable.

The saponification of the yarns and films may be car ried out continuously or discontinuously. The yarns and films may be subjected to tension during the saponifica tion.

A particularly advantageous method of carrying out the invention when the saponification must be continuously performed consists in extruding the molten polyvinyl acetate or other ester in the form of yarns .or films, and saponifying the latter continuously by passing them through thesaponifying bath while they are subjected 'to a tension capable of producing molecular orientationyarns or films obtainedby spinning molten polyvinyl ester is that these yarns or films are thereby obtained in absolutely anhydrous form, which is necessary for efiicient saponification by means of the alcoholate baths, and for the maintenance of their activity.

If the saponification is not to be effected under tension, it may be performed discontinuously by immersing skeins of yarns or coils of films having non-contiguous turns, so as to permit circulation of the bath between them.

It is possible to reduce the water-solubility of the polyvinyl alcohol yarns and films obtained in accordance with the invention, either by fixing some of the hydroxyl groups by means of an aldehyde, such as formaldehyde, or by producing cross-linking therein by one or more of the following means: heat, reaction with polyfunctional aldehydes such as glyoxal, or with polyisocyanates, passage through an alcoholic solution of an alcoholate of a poly valent metal, e.g. aluminium ethylate.

These treatments for producing cross-linking of the yarns and films of polyvinyl alcohol which are obtained in accordance with the invention are preferably applied while the yarns or films are subjected, as during the saponification to sufiicient tension to produce an orientation of their molecular structure. This enhances the effects of the cross-linking, in particular increase in resilience and water-insolubility of the yarns and films.

The main advantageof this procedure starting. with The following example illustrates the invention without limiting it:

Example A polyvinyl aceta-te having a viscosity of 9 centipoises as hereinbefore defined is extruded in the molten state at a temperature of 190 C. in the form of a filament 0.3 mm. in diameter, and then stretched by 200% at a temperature of 70 0., whereby its diameter is reduced. to about 0.10 mm. This stretched yarn then passes successively through three methanol baths containing 12% of sodium methylate (5% of sodium), the first bath being at 20 C., the second at 35 C. and the third at 60 C., and the speed of travel being such that the film remains in each bath for a period of 30 seconds.

During this operation, the yarn is maintained under a tension of 0.100 kg. per mm. of cross section. On leaving the bath, it is wiped to remove the liquid adhering to its surface, whereafter it is Washed in methanol. It then constitutes a polyvinyl alcohol yarn soluble in hot water, of high mechanical strength and having a distinct orientation visible under the polariscope.

We claim:

1. Process for the production of polyvinyl alcohol shaped articles selected from the group which consists of monoand multi-filament yarns and films, which comprises subjecting a solid shaped article of the same form consisting of a polyvinyl ester of molecular weight such that the viscosity of a 5% by weight solution thereof in a mixture of 15 volumes of 95% by volume alcohol and 85 volumes of ethyl acetate at 20 C. is at least 8 centipoises to the saponifying action of an externally applied solution of an alkali metal alcoholate in a solvent consisting of. methanol, the concentration of the said solution being at least 8.5 molar percent.

2. Process for the production of polyvinyl alcohol shaped articles selected from the'group which consists of monoand multi-filament yarns and fihns, which comprises subjecting a solid shaped article of the same form consisting of a polyvinyl acetate of molecular weight such that the viscosity of a 5% by weight solution thereof in a mixture of 15 volumes of 95% by volume alcohol and 85 volumes of ethyl acetate at 20 C., is at least 8 centipoises to the saponifying action of an externally applied solution of an alkali metal alcoholate in a solvent consisting of methanol, the concentration of the said solution being at least 8.5 molar percent.

3. Process for the production of polyvinyl alcohol shaped articles selected from the group which consists of monoand multi-filament yarns and films, which comprises subjecting a solid shaped article of the same form consisting of a polyvinyl acetate of molecular weight such that the viscosity of a 5% by weight solution thereof in a mixture of 15 volumes of 95% by volume alcohol and 85 volumes of ethyl acetate at 20 C. is at least 8 centipoises to the saponifying action of an externally applied solution of an alkali metal alcoholate having 1-4 carbon atoms in the molecule in a solvent consisting of methanol, the concentration of the said solution being at least 8 molar percent.

4. Process for the production of polyvinyl alcohol shaped articles selected from the group which consists of monoand multi-filament yarns and films, which comprises subjecting a solid shaped article of the same formconsisting of a polyvinyl acetate of molecular weight such that the viscosity of a 5% by weight solution thereof in a mixture of 15 volumes of 95% by volume alcohol and 85 volumes of ethyl acetate at 20 C. is at least 8 centipoises to the saponifying action of an externally applied 8.5-45 molar percent solution of an alkali metal alcoholate having 1-4 carbon atoms in the molecule in a solvent consisting of methanol at a temperature of 5. Process according to claim 4, which comprises subjecting the shaped article to the saponifying action of the said solution in two stages, the first at a temperature of 20-25 C. and the second at a temperature of 40-70 C. v

6. Process according to claim 4, which comprises stretching the shaped article while it is beingsubjected to the saponifying action of the said solution.

7. Process according to claim 4, which comprises subjecting the shaped article to the saponifying actionof the said solution continuously with its production by a melt extrusion method.

8. Process according to claim 1, wherein the alkali metal alcoholate is sodium methoxide.

9. Process according to claim 2,, wherein the alkali metal alcoholate is sodium methoxide.

10. Process according to claim 4, wherein the alkali metal alcoholate is sodium methoxide. Y

11. Process according-to claim 6, wherein the alkali metal alcoholate is sodium methoxide.

References Cited in the file of this patent UNITED STATES PATENTS, 

1. PROCESS FOR THE PRODUCTION OF POLYVINYL ALCOHOL SHAPED ARTICLES SELECTED FROM THE GROUP WHICH CONSISTS OF MONO- AND MULTI-FILAMENT YARNS AND FILMS, WHICH COMPRISES SUBJECTING A SOLID SHAPED ARTICLE OF THE SAME FORM CONSISTING OF A POLYVINYL ESTER OF MOLECULAR WEIGHT SUCH THAT THE VISCOSITY OF A 5% BY WEIGHT SOLUTION THEREOF IN A MIXTURE OF 15 VOLUMES OF 95% BY VOLUME ALCOHOL AND 85 VOLUMES OF ETHYL ACETATE AT 20* C. IS AT LEAST 8 CENTIPOISES TO THE SAPONIFYING ACTION OF AN EXTERNALLY APPLIED SOLUTION OF AN ALKALI METAL ALCOHOLATE IN A SOLVENT CONSISTING OF METHANOL, THE CONCENTRATION OF THE SAID SOLUTION BEING AT LEAST 8.5 MOLAR PERCENT. 